1explain_vprintf(3) Library Functions Manual explain_vprintf(3)
2
6 explain_vprintf - explain vprintf(3) errors
7
9 #include <libexplain/vprintf.h>
10 const char *explain_vprintf(const char *format, va_list ap);
11 const char *explain_errno_vprintf(int errnum, const char *format,
12 va_list ap);
13 void explain_message_vprintf(char *message, int message_size, const
14 char *format, va_list ap);
15 void explain_message_errno_vprintf(char *message, int message_size, int
16 errnum, const char *format, va_list ap);
17
19 These functions may be used to obtain explanations for errors returned
20 by the vprintf(3) system call.
21 explain_vprintf
23 const char *explain_vprintf(const char *format, va_list ap);
24 The explain_vprintf function is used to obtain an explanation of an
26 error returned by the vprintf(3) system call. The least the message
27 will contain is the value of strerror(errno), but usually it will do
28 much better, and indicate the underlying cause in more detail.
29 The errno global variable will be used to obtain the error value to be
31 decoded.
32 format The original format, exactly as passed to the vprintf(3) system
34 call.
35 ap The original ap, exactly as passed to the vprintf(3) system
37 call.
38 Returns:
40 The message explaining the error. This message buffer is shared
41 by all libexplain functions which do not supply a buffer in
42 their argument list. This will be overwritten by the next call
43 to any libexplain function which shares this buffer, including
44 other threads.
45 Note: This function is not thread safe, because it shares a return buf‐
47 fer across all threads, and many other functions in this library.
48 Example: This function is intended to be used in a fashion similar to
50 the following example:
51 errno = EINVAL;
52 int result = vprintf(format, ap);
53 if (result < 0)
54 {
55 fprintf(stderr, "%s\n", explain_vprintf(format, ap));
56 exit(EXIT_FAILURE);
57 }
58 The above code example is available pre‐packaged as the
60 explain_vprintf_or_die(3) function.
61 explain_errno_vprintf
63 const char *explain_errno_vprintf(int errnum, const char *format,
64 va_list ap);
65 The explain_errno_vprintf function is used to obtain an explanation of
67 an error returned by the vprintf(3) system call. The least the message
68 will contain is the value of strerror(errno), but usually it will do
69 much better, and indicate the underlying cause in more detail.
70 errnum The error value to be decoded, usually obtained from the errno
72 global variable just before this function is called. This is
73 necessary if you need to call any code between the system call
74 to be explained and this function, because many libc functions
75 will alter the value of errno.
76 format The original format, exactly as passed to the vprintf(3) system
78 call.
79 ap The original ap, exactly as passed to the vprintf(3) system
81 call.
82 Returns:
84 The message explaining the error. This message buffer is shared
85 by all libexplain functions which do not supply a buffer in
86 their argument list. This will be overwritten by the next call
87 to any libexplain function which shares this buffer, including
88 other threads.
89 Note: This function is not thread safe, because it shares a return buf‐
91 fer across all threads, and many other functions in this library.
92 Example: This function is intended to be used in a fashion similar to
94 the following example:
95 errno = EINVAL;
96 int result = vprintf(format, ap);
97 if (result < 0)
98 {
99 int err = errno;
100 fprintf(stderr, "%s\n", explain_errno_vprintf(err, format,
101 ap));
102 exit(EXIT_FAILURE);
103 }
104 The above code example is available pre‐packaged as the
106 explain_vprintf_or_die(3) function.
107 explain_message_vprintf
109 void explain_message_vprintf(char *message, int message_size, const
110 char *format, va_list ap);
111 The explain_message_vprintf function is used to obtain an explanation
113 of an error returned by the vprintf(3) system call. The least the mes‐
114 sage will contain is the value of strerror(errno), but usually it will
115 do much better, and indicate the underlying cause in more detail.
116 The errno global variable will be used to obtain the error value to be
118 decoded.
119 message The location in which to store the returned message. If a suit‐
121 able message return buffer is supplied, this function is thread
122 safe.
123 message_size
125 The size in bytes of the location in which to store the
126 returned message.
127 format The original format, exactly as passed to the vprintf(3) system
129 call.
130 ap The original ap, exactly as passed to the vprintf(3) system
132 call.
133 Example: This function is intended to be used in a fashion similar to
135 the following example:
136 errno = EINVAL;
137 int result = vprintf(format, ap);
138 if (result < 0)
139 {
140 char message[3000];
141 explain_message_vprintf(message, sizeof(message), format,
142 ap);
143 fprintf(stderr, "%s\n", message);
144 exit(EXIT_FAILURE);
145 }
146 The above code example is available pre‐packaged as the
148 explain_vprintf_or_die(3) function.
149 explain_message_errno_vprintf
151 void explain_message_errno_vprintf(char *message, int message_size, int
152 errnum, const char *format, va_list ap);
153 The explain_message_errno_vprintf function is used to obtain an expla‐
155 nation of an error returned by the vprintf(3) system call. The least
156 the message will contain is the value of strerror(errno), but usually
157 it will do much better, and indicate the underlying cause in more
158 detail.
159 message The location in which to store the returned message. If a suit‐
161 able message return buffer is supplied, this function is thread
162 safe.
163 message_size
165 The size in bytes of the location in which to store the
166 returned message.
167 errnum The error value to be decoded, usually obtained from the errno
169 global variable just before this function is called. This is
170 necessary if you need to call any code between the system call
171 to be explained and this function, because many libc functions
172 will alter the value of errno.
173 format The original format, exactly as passed to the vprintf(3) system
175 call.
176 ap The original ap, exactly as passed to the vprintf(3) system
178 call.
179 Example: This function is intended to be used in a fashion similar to
181 the following example:
182 errno = EINVAL;
183 int result = vprintf(format, ap);
184 if (result < 0)
185 {
186 int err = errno;
187 char message[3000];
188 explain_message_errno_vprintf(message, sizeof(message), err,
189 format, ap);
190 fprintf(stderr, "%s\n", message);
191 exit(EXIT_FAILURE);
192 }
193 The above code example is available pre‐packaged as the
195 explain_vprintf_or_die(3) function.
196
198 vprintf(3)
199 formatted output conversion
200 explain_vprintf_or_die(3)
202 formatted output conversion and report errors
203
205 libexplain version 1.4
206 Copyright (C) 2010 Peter Miller
207 explain_vprintf(3)